The power of 600 kW for the Mig-25 radar is mentioned in "Modern Air Combat" by Bill Gunston, a book of the 1980s. Not sure if this is correct. I do not remember the source where I read about the peak power of the AN/ASG-18. However it used two TWTs in tandem to obtain the highest possible detection range with its 40 inch dish.
There was more than one version of the MiG-25, and more than one radar used. I think you are probably talking about the Smerch-A, NATO reporting name Foxfire. The Foxfire radar of the -25A was one of the most powerful radars installed on any fighter any time.
But lets keep in mind the intended target of that airframe and radar, the B-70. The Foxfire radar was intended to track the Valkyrie at very long distances and in the presence of heavy countermeasures activity. It would have to "burn through" heavy jamming. And that takes heavy power.
Plus, the Russians often adopted a brute force approach were the west would have relied more on finesse.
And yes, several sources, including US mil sources (example "The MiG-25, A Very High Speed Interceptor and Reconnaissance Aircraft", Foreign Technology Division, Air Force Systems Command) list the Foxfire as 600 kW peak power.
But the Russians and the US would not have done things the same. Different thought processes arrive at different answers to similar problems. And it would really surprise me if the ASG-18 was in the same power range as the Foxfire, that just doesn't fit well with US trends of the time, and it certainly does not fit with the system that the ASG-18 eventually morphed into.
Of course stealth considerations are an important driver to limit power output but maximum detection range still seems to be a primary requirement for at least a certain class of "strategic" fighter aircraft like Mig-31, Su-27 follow-on series, F-22, etc. It would generally be interesting to know if modern high end fighter aircraft radar range performance is really the maximum possible or if it is more a balance between stealth and detection range.
If you are a stealthy platform (and all modern designs give some nod to detectability) you are probably going to limit your use of radar, relying more heavily on other sensors. If you do use radar it is going to be something like a cognitive LPI system, if possible. Raw power level is going to be less a factor than other waveform parameters. It is better to have the power available and turn the volume down, than to need it and not have it.
This is one of many reason magnetrons (and similar sources) have fallen out of favor. You tend to run a magnetron at max peak power all the time. But Klystrons and TWTs can be turned down in the linear region and you can control the output power better, turning it up when you need it and down when you don't.
Regardless, your radar, any radar, can be detected far beyond its useful, to you, range. Radars always tell other people as much about you as your radar tells you about them.
As for maximum ranges, this is more than a simple power problem. Your design parameters will determine the maximum range of your radar, and transmitter power is only one factor. You start with a desired probability of detection on a specific RCS sized target, the physical space and power you have available on the platform, the technologies and price points that are acceptable, and you work backwards from there.
Is there really any need to track a -10 dBsm target at 200 miles, with all the associated transmitter power and antenna size (this means size and weight on the aircraft, taking away from other systems or even basic fuel load), if you can only engage it at 40 miles? All that really does is tell the enemy where you are, long before you can do anything about them. It would be far better to use another information source, maybe a data link from a battle space management system, until a target is in range that you can do something about it.
However, lets think bigger picture. Why use that size and weight for only a radar transmitter? Would it be possible to combine functions, so that your radar transmitter is also part of your active ECM suite? With modern phased array you can form beams with your antenna, pointing in multiple directions in quick succession. Do they all have to be radar beams?
Thinking further afield, if you are stealthy platform, why give yourself away with a high power transmitter at all unless you have to? Why not use someone else's high power transmitter, say an AWACs, in a bistatic application? Their huge transmitter lights up the sky, your receiver uses that reflected energy to track targets.
No fighter is built primarily for 1 V 1 these days. Many V Many and integrated battlespaces are the way forward. Fighter weapons systems think as much about how to support / receive support from others as how to kill the enemy.
T!
